Protected air-activated organotin catalysts for polyurethane synthesis and processes therefore

ABSTRACT

This invention relates to a protected organotin-based catalyst system for polyurethane synthesis that is useful in coatings applications. The catalyst has a formula according to; R 1   a R 2   b R 3   c Sn[CH(OX)R 4 ] d , wherein R 1 , R 2 , and R 3  are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group, R 4  represents an optionally substituted hydrocarbyl or optionally substituted aryl group. a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid-labile or moisture-labile protecting group. When a coating mixture comprising the catalyst is sprayed and/or applied to a substrate as a thin film in air, the catalyst is activated. For solvent-based refinish systems comprising hydroxyl and isocyanate species at high solids levels, the catalyst system therefore provides extended viscosity stability, i.e., pot life.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/751,229 filed on Dec. 16, 2005 which are hereby incorporated by references in its entirely.

FIELD OF INVENTION

This invention relates to protected organotin-based catalyst systems that are useful in coatings applications, and to latent, air-activated catalysts for polyurethane synthesis. The latent catalyst has low activity in the absence of oxygen, and can retain its latency during storage in isocyanate for several days.

TECHNICAL BACKGROUND

The present invention relates to the use of tin derivatives as polycondensation catalysts. The use of tin salts as polycondensation catalysts has been known for several decades. See F. Hostettler and E. F. Cox (1960) Ind. Eng. Chem. 52:609. These derivatives are used in particular for the condensation of silicones and for the production of polyurethanes.

In the last few years demand has increased for coating systems capable of both extended viscosity stability, that is pot life, and high productivity. High productivity refers to the ability to produce the desired polymer, or polycondensate, as quickly as possible under the implementation conditions, for example, in automotive refinish applications.

For environmental reasons, governmental agencies and users complying with governmental regulations worldwide have exerted pressure to develop coating systems having lower levels of volatile organic compounds (VOC's). A key to resolving these issues is through the dramatic reduction or the elimination of solvents used in coatings. However, reducing the amount of solvent will negatively affect pot life, if cure times remain constant, unless a latent catalyst system is developed.

Jousseaume, B. et al., (“Air Activated Organotin Catalysts for Silicone Curing and Polyurethane Preparation” (1994) Organometallics 13:1034), and Bernard, J. M. et al. (U.S. Pat. No. 6,187,711) describe the use of distannanes as latent catalysts, e.g. Bu₂(AcO)SnSn(OAc)Bu₂. Upon exposure to air, such species oxidize to give distannoxanes, e.g. Bu₂(AcO)SnOSn(OAc)Bu₂, which are known to be highly active for urethane formation. However, the carboxylate-substituted distannanes are themselves catalysts for the reaction, and have been reported to be “relatively stable in air”, which suggests that oxidation to form an active catalyst is slow. See U.S. Pat. No. 3,083,217 to Sawyer et al. UV light appears to be necessary in order to induce oxidation at an appreciable rate in these distannanes. Thus, there exists a need for a catalyst precursor that, in the absence of air, is a very poor catalyst and yet, upon exposure to air, rapidly forms a highly active catalyst that allows for rapid cure.

Co-owned and co-pending U.S. patent application Ser. Nos. 11/154,387 and 11/154,224 describe air activated organotin catalysts without protecting groups. While the catalysts described in these applications are latent, i.e. active only in the presence of air, they lose their latency upon prolonged exposure to isocyanate. As a result, they cannot be stored in isocyanate. Moreover, because they are air-sensitive, they must be kept from air until spray application. The present invention describes how the catalysts of U.S. patent application Ser. Nos. 11/154,387 and 11/154,224 can be protected using labile protecting groups, which render them stable in air and stable in isocyanate, at least for several days. Upon contacting a isocyanate solution of the protected catalyst with an alcohol, optionally in the presence of acid, the catalyst is deprotected and can be activated by air during the spray application process.

Co-owned and co-pending U.S. Pat. Application No. 60/751,232 (CL-3032) describes the catalysts used in the processes of the present invention, and is hereby incorporated by reference in its entirety.

SUMMARY OF INVENTION

This invention describes the use of protected alpha-hydroxystannane compounds as catalysts for formation of crosslinked polyurethanes from polyols and isocyanates. In some cases the protected alpha-hydroxystannane compound is a latent catalyst, the catalytic activity of which is greatly increased when a coating mixture comprising the catalyst is sprayed and/or applied to a substrate as a thin film in an oxygen containing atmosphere, e.g. air. For solvent-based coating systems comprising hydroxyl and isocyanate species at high solids levels, a latent catalyst system provides extended viscosity stability, i.e., pot life, prior to application.

The present catalyst includes tin compounds that are inert or relatively inactive until they are contacted with an alcohol-containing coating mixture that may optionally contain acid, and until the coating mixture is actually applied to the substrate in an oxygen containing atmosphere. The present protected tin catalyst, when placed under coating application conditions, e.g. spraying with a spray gun, undergoes a chemical reaction to yield derivatives that are active under these conditions. Moreover, in one aspect of the present invention, in subjecting the present catalyst derivatives to oxygen in the presence of moisture and/or alcohols and, optionally, in the presence of acid, they provide further present derivatives that are also active as polycondensation catalysts. Another aspect of the present invention is to provide extended pot life coating mixtures that rapidly condense under the conditions of application.

The present catalysts are also useful for polycondensation reactions to form polysilicones, and can provide extended shelf life in these systems.

This invention provides a first embodiment of a catalyst having the formula of R¹ _(a)R² _(b)R³ _(c)Sn[CH(OX)R⁴]_(d). R¹, R², and R³ are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group. R⁴ represents an represents an optionally substituted hydrocarbyl or optionally substituted aryl group. a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid or moisture-labile protecting group. Non-limiting examples of such protecting groups are C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.

The invention also provides a system comprising two parts A and B in which Part A comprises an isocyanate species and, optionally, an acid and Part B comprises a polyol and a catalyst described above as the first embodiment. In a different system embodiment Part A comprises a polyol and, optionally, an acid and part B comprises an isocyanate and a catalyst, described above as the first embodiment described above.

The present invention provides coatings that comprise the present catalysts and compounds in all the variations described above. The present coatings may be dissolved in at least one solvent and may be a clear, pigmented, metallized, basecoat, monocoat and/or primer coating composition. The present coating may be applied to a variety of substrates.

Besides the catalysts, compositions and coatings, the present invention also provides a process comprising the steps of:

(a) providing a catalyst of the formula R¹ _(a)R² _(b)R³ _(c)Sn[CH(OX)R⁴]_(d), wherein R¹, R², and R³ are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group. R⁴ represents an optionally substituted hydrocarbyl or optionally substituted aryl group. a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid or moisture-labile protecting group. Non-limiting examples of such protecting groups are C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.

(b) contacting at least one isocyanate with the catalyst of step (a) to form a blend;

(c) contacting the blend of step (b) to at least one polyol to form a mixture;

(d) optionally exposing the mixture of step (c) to air or a gas comprising oxygen.

An alternative aspect is that at least one polyol is contacted with the catalyst of step (a) to form a blend, followed by contacting the blend with at least isocyanate.

The present invention also provides a process for making a coating that comprises providing a present compound or catalyst; optionally adding an additive to form a mixture; optionally dissolving the present compound or catalyst into at least one solvent to form a mixture; and applying either the compound or catalyst or resultant mixture to a substrate.

The present invention also relates to novel compositions of the formulae Bu₃SnCH[OC(OMe)₂Me]Ph and Bu₃SnCH(OSiMe₃)Ph, where Bu represents a butyl group, Me represents a methyl group and Ph represents a phenyl group.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “polymers” refer to entities with number average molecular weight from about 100 to about 100,000. Preferably, the number average molecular weight of the polymers is from about 100 to about 10000.

As used herein, “oligomers” refer to polymers that have a number average molecular weight less than about 3000.

As used herein, “air” is defined as an oxygen containing gas.

This invention describes the use of alpha-hydroxystannane compounds comprising protecting groups as catalysts for formation of crosslinked polyurethanes from polyols and isocyanates. The tin-based catalysts are of the general formula: R¹ _(a)R² _(b)R³ _(c)Sn[CH(OX)R⁴]_(d)

wherein R¹, R², and R³ are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group. R⁴ represents an optionally substituted hydrocarbyl or optionally substituted aryl group. a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid or moisture-labile protecting group. Non-limiting examples of such protecting groups are C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.

Typical trialkylsilyl groups suitable for this invention are trimethylsilyl, triethylsilyl, tirisopropylsilyl, dimethylisopropylsilyl, dimethyl-tert-butylsilyl and the like.

It has been found that catalysts of the above formula are air stable and stable in isocyanate, at least for several days. Upon mixing of urethane forming components the catalysts undergo deprotection, i.e., loss of the acid or moisture-labile protecting group, and may become air-sensitive. Indeed, it has been found that some catalysts of the above formula are far more active for the crosslinking of multifunctional alcohols and isocyanates to give polyurethanes in the presence of oxygen (air) than in its absence.

The present invention demonstrates that by blocking the α-hydroxybenzyl ligand with a labile protecting group, the catalyst is stabilized towards isocyanate and air, until contact with polyol (and optionally acid), which can cause deprotection to occur with regeneration of the latent catalyst.

While not wishing to be bound by a particular theory it is, for example, hypothesized that upon contact with moisture or alcohol a protecting group may be lost from a catalyst of the formula R¹ _(a)R² _(b)R³ _(c)Sn[CH(OX)R⁴]_(d) where R4 is optionally substituted aryl, to form a catalyst of the formula R¹ _(a)R² _(b)R³ _(c)Sn[CH(OH)R⁴]_(d). The deprotection reaction may in some instances need to be catalyzed by acid in order to proceed at a reasonable rate. Upon exposure to air the deprotected alpha-hydroxybenzylstannane complex is oxidized by molecular oxygen to give a tin carboxylate, which is highly active for the crosslinking reaction between the polyol and the isocyanate. For example, air oxidation of the alpha-hydroxybenzylstannane compound shown below results in formation of the corresponding tin benzoate, which is a crosslinking catalyst. Other side products, such as benzaldehyde, are also formed.

Polyols are generally defined as polymeric or oligomeric organic species with at least two hydroxy functionalities. An example of the isocyanate with functional groups capable of reacting with hydroxyl is as follows:

wherein R₅ is a hydrocarbyl structure.

Examples of suitable polyisocyanates include aromatic, aliphatic or cycloaliphatic di-, tri- or tetra-isocyanates, including polyisocyanates having isocyanurate structural units, such as, the isocyanurate of hexamethylene diisocyanate and isocyanurate of isophorone diisocyanate; the adduct of 2 molecules of a diisocyanate, such as, hexamethylene diisocyanate and a diol such as, ethylene glycol; uretidiones of hexamethylene diisocyanate; uretidiones of isophorone diisocyanate or isophorone diisocyanate; the adduct of trimethylol propane and meta-tetramethylxylene diisocyanate.

Additional examples of suitable polyisocyanates include 1,2-propylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, 2,4,4-trimethyl hexamethylene diisocyanate, dodecamethylene diisocyanate, omega, omega-dipropyl ether diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4-methyl-1,3-diisocyanatocyclohexane, trans-vinylidene diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 3,3′-dimethyl-dicyclohexylmethane-4,4′-diisocyanate, a toluene diisocyanate, 1,3-bis(1-isocyanato1-methylethyl)benzene, 1,4-bis(1-isocyanato-1-methylethyl)benzene, 1,3-bis(isocyanatomethyl)benzene, xylene diisocyanate, 1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene, 1,5-dimethyl-2,4-bis(2-isocyanatoethyl)benzene, 1,3,5-triethyl-2,4-bis(isocyanatomethyl)benzene, 4,4′-diisocyanatodiphenyl, 3,3′-dichloro-4,4′-diisocyanatodiphenyl, 3,3′-diphenyl-4,4′-diisocyanatodiphenyl, 3,3′-dimethoxy-4,4′-diisocyanatodiphenyl, 4,4′-diisocyanatodiphenylmethane, 3,3′-dimethyl-4,4′-diisocyanatodiphenyl methane, a diisocyanatonaphthalene, polyisocyanates having isocyanaurate structural units, the adduct of 2 molecules of a diisocyanate, such as, hexamethylene diisocyanate or isophorone diisocyanate, and a diol such as ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate and 1 molecule of water (available under the trademark Desmodur® N from Bayer Corporation of Pittsburgh, Pa.), the adduct of 1 molecule of trimethylol propane and 3 molecules of toluene diisocyanate (available under the trademark Desmodur® L from Bayer Corporation), the adduct of 1 molecule of trimethylol propane and 3 molecules of isophorone diisocyanate, compounds such as 1,3,5-triisocyanato benzene and 2,4,6-triisocyanatotoluene, and the adduct of 1 molecule of pentaerythritol and 4 molecules of toluene diisocyanate.

A specific example of an isocyanate capable of reacting with hydroxyl groups is Desmodur® 3300 from Bayer. The idealized structure of Desmodur® 3300 is given as follows (also, pentamer, heptamer and higher molecular weight species can be present):

In any of the compositions herein, the polymeric materials may range from relatively low to relatively high molecular weight. It is preferred that they be of relatively low molecular weight so as to keep the viscosity of the compositions before crosslinking low, so as to avoid or minimize the need for solvent(s).

Other materials, which may optionally be present in the compositions and processes, include one or more solvents (and are meant to act only as solvents). These preferably do not contain groups such as hydroxyl or primary or secondary amino.

The present compositions, and the process for making them crosslinked, are useful as encapsulants, sealants, and coatings, especially transportation (automotive) and industrial coatings. As transportation coatings, the present compositions are useful as both OEM (original equipment manufacturer) and automotive refinish coatings. They may also be used as primer coatings. They often cure under ambient conditions to tough hard coatings and may be used as one or both of the so-called base coat and clear coat automotive coatings. This makes them particularly useful for repainting of transportation vehicles in the field.

Depending on use, the compositions and the materials used in the present processes may contain other materials. For example, when used as encapsulants and sealants, the compositions may contain fillers, pigments, and/or antioxidants.

When used as coatings, the present compositions contain typically added ingredients known in the art, which are described below. In particular there may be other polymers (especially of low molecular weight, “functionalized oligomers”) which are either inert or have functional group other than hydroxyl or isocyanate and also react with other reactive materials in the coating composition.

Representative of the functionalized oligomers that can be employed as components or potential crosslinking agents of the coatings are the following:

Hydroxyl Oligomers: The reaction product of multifunctional alcohols such as pentaerythritol, hexanediol, trimethylol propane, and the like, with cyclic monomeric anhydrides such as hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and the like produce acid oligomers These acid oligomers are further reacted with monofunctional epoxies such as butylene oxide, propylene oxide, and the like to form hydroxyl oligomers.

Silane Oligomers: The above hydroxyl oligomers further reacted with isocyanato propyltrimethoxy silane.

Epoxy Oligomers: The diglycidyl ester of cyclohexane dicarboxylic acid, such as Araldite® CY-184 from Ciba Geigy, and cycloaliphatic epoxies, such as ERL®-4221, and the like from Union Carbide.

Aldimine Oligomers: The reaction product of isobutyraldehyde with diamines such as isophorone diamine, and the like.

Ketimine Oligomers: The reaction product of methyl isobutyl ketone with diamines such as isophorone diamine.

Melamine Oligomers Commercially available melamines such as CYMEL® 1168 from Cytec Industries, and the like.

AB-Functionalized Oligomers: Acid/hydroxyl functional oligomers made by further reacting the above acid oligomers with 50%, based on equivalents, of monofunctional epoxy such as butylene oxide or blends of the hydroxyl and acid oligomers mentioned above or any other blend depicted above.

CD-Functionalized Crosslinkers: Epoxy/hydroxyl functional crosslinkers such as the polyglycidyl ether of Sorbitol DCE-358® from Dixie Chemical or blends of the hydroxyl oligomers and epoxy crosslinkers mentioned above or any other blend as depicted above.

The compositions of this invention may additionally contain a binder of a noncyclic oligomer, i.e., one that is linear or aromatic. Such noncyclic oligomers can include, for instance, succinic anhydride- or phthalic anhydride-derived moieties in hydroxyl oligomers.

Preferred functionalized oligomers have weight average molecular weight not exceeding about 3,000 with a polydispersity not exceeding about 1.5; more preferred oligomers have molecular weight not exceeding about 2,500 and polydispersity not exceeding about 1.4; most preferred oligomers have molecular weight not exceeding about 2,200, and polydispersity not exceeding about 1.25. Other additives also include polyaspartic esters, which are the reaction product of diamines, such as, isopherone diamine with dialkyl maleates, such as, diethyl maleate.

The coating compositions may be formulated into high solids coating systems dissolved in at least one solvent. The solvent is usually organic. Preferred solvents include aromatic hydrocarbons such as petroleum naphtha or xylenes; ketones such as methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone or acetone; esters such as butyl acetate or hexyl acetate; and glycol ether esters such as propylene glycol monomethyl ether acetate.

The coating compositions can also contain a binder of an acrylic polymer of weight average molecular weight greater than 3,000, or a conventional polyester such as SCD®-1040 from Etna Product Inc. for improved appearance, sag resistance, flow and leveling and such. The acrylic polymer can be composed of typical monomers such as acrylates, methacrylates, styrene and the like and functional monomers such as hydroxy ethyl acrylate, glycidyl methacrylate, or gamma methacrylylpropyl trimethoxysilane and the like.

The coating compositions can also contain a binder of a dispersed acrylic component which is a polymer particle dispersed in an organic media, which particle is stabilized by what is known as steric stabilization. Hereafter, the dispersed phase or particle, sheathed by a steric barrier, will be referred to as the “macromolecular polymer” or “core”. The stabilizer forming the steric barrier, attached to this core, will be referred to as the “macromonomer chains” or “arms”.

The dispersed polymer contains about 10 to 90%, preferably 50 to 80%, by weight, based on the weight of the dispersed polymer, of a high molecular weight core having a weight average molecular weight of about 50,000 to 500,000. The preferred average particle size is 0.1 to 0.5 microns. The arms, attached to the core, make up about 10 to 90%, preferably 10 to 59%, by weight of the dispersed polymer, and have a weight average molecular weight of about 1,000 to 30,000, preferably 1,000 to 10,000. The macromolecular core of the dispersed polymer is comprised of polymerized acrylic monomer(s) optionally copolymerized with ethylenically unsaturated monomer(s). Suitable monomers include styrene, alkyl acrylate or methacrylate, ethylenically unsaturated monocarboxylic acid, and/or silane-containing monomers. Such monomers as methyl methacrylate contribute to a high Tg (glass transition temperature) dispersed polymer, whereas such “softening” monomers as butyl acrylate or 2-ethylhexylacrylate contribute to a low Tg dispersed polymer. Other optional monomers are hydroxyalkyl acrylates or methacrylates or acrylonitrile. Optionally, the macromolecular core can be crosslinked through the use of diacrylates or dimethacrylates such as allyl methacrylate or post reaction of hydroxyl moieties with polyfunctional isocyanates. The macromonomer arms attached to the core can contain polymerized monomers of alkyl methacrylate, alkyl acrylate, each having 1 to 12 carbon atoms in the alkyl group, as well as glycidyl acrylate or glycidyl methacrylate or ethylenically unsaturated monocarboxylic acid for anchoring and/or crosslinking. Typically useful hydroxy-containing monomers are hydroxy alkyl acrylates or methacrylates as described above.

The coating compositions can also contain conventional additives such as pigments, stabilizers, rheology control agents, flow agents, toughening agents and fillers. Such additional additives will, of course, depend on the intended use of the coating composition. Fillers, pigments, and other additives that would adversely affect the clarity of the cured coating may not typically be included if the composition is intended as a clear coating.

The coating compositions are typically applied to a substrate by conventional techniques such as spraying, electrostatic spraying, roller coating, dipping or brushing. The present formulations are particularly useful as a clear coating for outdoor articles, such as automobile and other vehicle body parts. The substrate is generally prepared with a primer and or a color coat or other surface preparation prior to coating with the present compositions.

A layer of a coating composition is cured under ambient conditions in the range of 30 minutes to 24 hours, preferably in the range of 30 minutes to 3 hours to form a coating on the substrate having the desired coating properties. One of skill in the art appreciates that the actual curing time depends upon the thickness of the applied layer and on any additional mechanical aids, such as, fans that assist in continuously flowing air over the coated substrate to accelerate the cure rate. If desired, the cure rate may be further accelerated by baking the coated substrate at temperatures generally in the range of from about 60° C. to 150° C. for a period of about 15 to 90 minutes. The foregoing baking step is particularly useful under OEM (Original Equipment Manufacture) conditions.

Catalysts of this invention can be used for coating applications and generally in areas where curing of polyurethane is required, for example in the adhesive industry and related applications. These compositions are also suitable as clear or pigmented coatings in industrial and maintenance coating applications.

The coating composition of the present invention is suitable for providing coatings on variety of substrates. The present composition is especially suitable for providing clear coatings in automotive OEM or refinish applications typically used in coating auto bodies. The coating composition of the present invention can be formulated in the form of a clear coating composition, pigmented composition, metallized coating composition, basecoat composition, monocoat composition or a primer. The substrate is generally prepared with a primer and or a color coat or other surface preparation prior to coating with the present compositions.

Suitable substrates for applying the coating composition of the present invention include automobile bodies, any and all items manufactured and painted by automobile sub-suppliers, frame rails, commercial trucks and truck bodies, including but not limited to beverage bodies, utility bodies, ready mix concrete delivery vehicle bodies, waste hauling vehicle bodies, and fire and emergency vehicle bodies, as well as any potential attachments or components to such truck bodies, buses, farm and construction equipment, truck caps and covers, commercial trailers, consumer trailers, recreational vehicles, including but not limited to, motor homes, campers, conversion vans, vans, pleasure vehicles, pleasure craft snow mobiles, all terrain vehicles, personal watercraft, motorcycles, bicycles, boats, and aircraft. The substrate further includes industrial and commercial new construction and maintenance thereof; cement and wood floors; walls of commercial and residential structures, such office buildings and homes; amusement park equipment; concrete surfaces, such as parking lots and drive ways; asphalt and concrete road surface, wood substrates, marine surfaces; outdoor structures, such as bridges, towers; coil coating; railroad cars; printed circuit boards; machinery; OEM tools; signage; fiberglass structures; sporting goods; golf balls; and sporting equipment.

Abbreviations

Me the methyl group —CH₃

Bu the butyl group —CH₂CH₂CH₂CH₃

Ph phenyl group

TPO thermoplastic olefin

EXPERIMENTAL EXAMPLES

A BK speed drying recorder conforming to ASTM D 5895 was used to measure the drying times of coatings generated using the above-disclosed catalysts. The 12-hour setting was used. In the examples below, the “Stage 3” time corresponds to the surface—dry time when the track made by the needle transitions from an interrupted track to a smooth thin surface scratch. “Stage 4” time corresponds to the final drying time when the needle no longer penetrates the film surface. Gel time corresponds to the time in minutes following activation at which flow is no longer observed in a coating mixture.

The swell ratio of a free film, removed from a sheet of TPO, was determined by swelling the film in methylene chloride. The free film was placed between two layers of aluminum foil and using a LADD punch, a disc of about 3.5 mm in diameter was punched out of the film and the foil was removed from the film. The diameter of the unswollen film (D_(o)) was measured using a microscope with a 10× magnification and a filar lens. Four drops of methylene chloride were added to the film and the film was allowed to swell for two seconds and then a glass slide was placed over the film and the swollen film diameter (D_(s)) was measured. The swell ratio was then calculated as follows: Swell Ratio=(D _(s))²/(D _(o))² The change in film hardness of the coating was measured with respect to time by using a Persoz hardness tester Model No. 5854 (ASTM D4366), supplied by Byk-Mallinckrodt, Wallingford, Conn. The number of oscillations (referred to as Persoz number) were recorded. Hardness was measured using a Fischerscope® hardness tester (the measurement is in Newton per mm²).

MEK solvent resistance was measured as follows. A coated panel was rubbed (100 times) with an MEK (methyl ethyl ketone) soaked cloth using a rubbing machine. Any excess MEK was wiped off. The panel was rated from 1-10. A rating of 10 means no visible damage to the coating. A rating of 9 means about 1 to 3 distinct scratches. A rating of 8 means about 4 to 6 distinct scratches. A rating of 7 means 7 to 10 distinct scratches. A rating of 6 means 10 to 15 distinct scratches with slight pitting or slight loss of color. A rating of 5 means 15 to 20 distinct scratches with slight to moderate pitting or moderate loss of color. A rating of 4 means scratches start to blend into one another. A rating of 3 means only a few undamaged areas between blended scratches. A rating of 2 means no visible signs of undamaged paint. A rating of 1 means complete failure i.e., bare spots are shown. The final rating was obtained by multiplying the number of rubs by the rating.

Water spot rating is a measure of how well the film is crosslinked early in the curing of the film. If water spot damage is formed on the film, this is an indication that the cure is not complete and further curing of the film is needed before the film can be wet-sanded or buffed or moved from the spray both.

The water spot rating was determined in the following manner: Coated panels are laid on a flat surface and deionized water was applied with a pipette at 1 hour timed intervals. A drop about ½ inch in diameter was placed on the panel and allowed to evaporate. The spot on the panel was examined for deformation and discoloration. The panel was wiped lightly with cheesecloth wetted with deionized water. This was followed by lightly wiping the panel dry with the cloth. The panel was then rated on a scale of 1 to 10. A rating of 10 was considered the best, i.e., there was no evidence of spotting or distortion of discoloration. A rating of 9 meant that water spotting barely detectable. A rating of 8 meant that there was a slight ring as a result of water spotting. A rating of 7 meant that there was very slight discoloration or slight distortion as a result of water spotting. A rating of 6 meant that there was a slight loss of gloss or slight discoloration as a result of water spotting. A rating of 5 meant that there was a definite loss of gloss or discoloration as a result of water spotting. A rating of 4 meant that there was a slight etching or definite distortion as a result of water spotting. A rating of 3 meant that there was a light lifting, bad etching or discoloration as a result of water spotting. A rating of 2 meant that there was a definite lifting as a result of water spotting. A rating of 1 meant that the film dissolved as a result of the water spotting.

As used in the following examples, “Polyol 1” comprised the structure shown below as 50% solids dissolved in methyl amyl ketone, butyl acetate, and propylene glycol methyl ether acetate.

The isocyanate species used in the examples below was Desmodur 3300A, an oligomer of hexamethylene diisocyanate which is commercially available from Bayer Incorporated, 100 Bayer Road, Pittsburgh, Pa. 15205-9741.

Synthesis of Bu₃SnCH(OH)Ph

Under nitrogen, a dry 250 mL round bottom flask was charged with 2.0 M isopropyl magnesium chloride in diethyl ether (20.6 mL, 41.2 mmol) and an additional 15 mL of diethyl ether added. To this stirred solution was added tributyltin hydride (10.0 g, 34.4 mmol) dropwise over a period of 10-15 min. The resulting reaction mixture was heated to reflux, stirred for 1 h, and then cooled down to 0° C. Benzaldehyde (4.0 g, 37.8 mmol) was then added dropwise over a period of approximately 10 min while maintaining the temperature at 0° C. The resulting reaction mixture was then heated to reflux and stirred for 1 h before cooling back down to room temperature. The reaction was then quenched by addition of approximately 15 mL aqueous ammonium chloride under nitrogen. The resulting mixture was filtered through a glass frit and the solids extracted with diethyl ether. The combined organic extracts were concentrated under vacuum and filtered through Florisil. The Florisil pad was washed further with hexane. The combined organic extracts were concentrated under vacuum to afford an oil. Chromatography on silica gel using 95/5 hexane/ethyl acetate as the eluent afforded 3.95 g of Bu₃SnCH(OH)Ph as a pale yellow oil. ¹H NMR (CDCl₃) δ 7.2 (t, 2H, H_(meta)), 7.1 d (d, 12H, H_(ortho)), 7.0 (t, 1H, H_(para)), 5.1 [d, 1H, CH(OH)], 1.7 [d, 1H, CH(OH)], 1.4-0.7 (m, 27H, Bu's); ¹¹⁹Sn NMR (CDCl₃) δ-25.0 relative to SnMe₄; ¹³C NMR (CDCl₃) δ 147.8 (C_(ipso)), 128.4 (C_(ortho) or C_(meta)), 124.6 (C_(para)), 122.9 C_(ortho) or C_(meta)), 71.3 [CH(OH)], 28.9 and 27.4 (CH₂'s), 13.6 (CH₃), 9.1 (CH₂).

Synthesis of Bu₃SnCH[OC(OMe)₂Me]Ph

Under nitrogen, a 25 mL round bottom flask with a magnetic stir bar was charged with Bu₃SnCH(OH)Ph (2.0 g, 5.0 mmol), trimethylorthoacetate (2.4 g, 20.0 mmol), and acetic acid (0.030 g, 0.25 mmol). The resulting solution was heated to reflux and stirred for approximately 2.5 h. It was then cooled to room temperature and concentrated under vacuum to afford Bu₃SnCH[OC(OMe)₂Me]Ph as a yellow oil. The crude material was used without further purification. ¹H NMR (CDCl₃) δ 7.2-6.9 (m, 5H, H_(aryl)), 5.2 5.1 [s, 1H, CH(OH)], 3.2 (s, 3H, OMe), 3.1 (s, 3H, OMe'), 1.4-0.7 (m, 30H, Bu's+Me).

Examples 1 and 4

In a nitrogen-filled glove box, either Bu₃SnCH(OH)Ph or Bu₃SnCH[OC(OMe)₂Me]Ph (250 mg) was dissolved in a mixture of Polyol 1 (23.7 g, 48.0 mmol OH) and Desmodur® 3300 (9.73 g, 50.4 mmol NCO). Approximately half of the sample was immediately taken outside the glove box and thus exposed to air. A sample of the air-exposed material was used to coat a 12″×1″ glass test strip for BK dry time tests (a film thickness of 150 μm was used). A stirbar was added to the remaining air-exposed material and it was stirred under air at ambient temperature, while the sample in the glove box was stirred under nitrogen. The observed gel times and BK4 dry times are in Table 1.

Examples 2 and 5

In a nitrogen-filled glove box, either Bu₃SnCH(OH)Ph or Bu₃SnCH[OC(OMe)₂Me]Ph (250 mg) was dissolved in Desmodur® 3300 (9.73 g, 50.4 mmol NCO) and allowed to sit overnight (˜18 h). The following morning, Polyol 1 (23.7 g, 48.0 mmol OH) was added to the mixture. Approximately half of the sample was then taken outside the glove box and thus exposed to air. A sample of the air-exposed material was used to coat a 12″×1″ glass test strip for BK dry time tests (a film thickness of 150 μm was used). A stirbar was added to the remaining air-exposed material and it was stirred under air at ambient temperature, while the sample in the glove box was stirred under nitrogen. The observed gel times and BK4 dry times are in Table 1.

Examples 3 and 6

In a nitrogen-filled glove box, either Bu₃SnCH(OH)Ph or Bu₃SnCH[OC(OMe)₂Me]Ph (250 mg) was dissolved in Polyol 1 (23.7 g, 48.0 mmol OH) and allowed to sit overnight (˜18 h). The following morning, Desmodur® 3300 (9.73 g, 50.4 mmol NCO) was added to the mixture. Approximately half of the sample was then taken outside the glove box and thus exposed to air. A sample of the air-exposed material was used to coat a 12″×1″ glass test strip for BK dry time tests (a film thickness of 150 μm was used). A stirbar was added to the remaining air-exposed material and it was stirred under air at ambient temperature, while the sample in the glove box was stirred under nitrogen. The observed gel times and BK4 dry times are in Table 1.

A comparison of Examples 1 and 2 shows that Bu₃SnCH(OH)Ph loses its latency after extended contact with Desmodur 3300® under nitrogen; i.e. the gel times under air and nitrogen are essentially identical. Moreover, it exhibits longer BK4 drytimes after extended contact with Desmodur 3300® and has thus lost much of its activity. However, it retains significant latency and much of its activity after extended contact with Polyol 1 (Example 3). Bu₃SnCH[OC(OMe)₂Me]Ph, on the other hand, retains most of its activity and latency after extended contact with Desmodur 3300® under nitrogen (Examples 4 and 5). Bu₃SnCH[OC(OMe)₂Me]Ph also shows improved latency and activity after extended contact with Polyol 1 under nitrogen (Example 6).

TABLE 1 Gel and BK4 Dry Times for Examples 1-6 BK4 Ex. No. Catalyst Gel Times Time Comments 1 Bu₃SnCH(OH)Ph 2 h (air) 3 h Sample freshly 0.629 mmol >8 h (N₂) prepared under N₂ 2 Bu₃SnCH(OH)Ph 2.8 h (air) >12 h Catalyst 0.629 mmol 3.1 h (N₂) contacted with Desmodur ® 3300 overnight under N₂ 3 Bu₃SnCH(OH)Ph 1.1 h (air) 2.5 h Catalyst 0.629 mmol 4.75 h (N₂) contacted with Polyol 1 overnight under N₂ 4 Bu₃SnCH[OC(OMe)₂Me]Ph 3.7 h (air) 8 h Sample freshly 0.515 mmol 6.5 h (N₂) prepared under N₂ 5 Bu₃SnCH[OC(OMe)₂Me]Ph 4.5 h (air) 10.6 h Catalyst 0.515 mmol 6.1 h (N₂) contacted with Desmodur ® 3300 overnight under N₂ 6 Bu₃SnCH[OC(OMe)₂Me]Ph 2.25 h (air) 4 h Catalyst 0.515 mmol 6.1 h (N₂) contacted with Polyol 1 overnight under N₂

Example 7 Synthesis of a Mixture of Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂, Bu₂[Ph(OH)CH]SnSn(Bu)₂Sn[CH(OH)Ph]Bu₂ and Bu₂Sn[CH(OH)Ph]₂, and Separation of the Mixture

This example illustrates the synthesis of a mixture of three alpha-hydroxybenzyl tin complexes and their separation by column chromatography. Preparation of lithium diisopropylamide (LDA): An oven-dried 250 mL round bottom flask was charged in the dry box with 5.19 g (51.4 mmol) of diisopropylamine and 25 mL of anhydrous THF. The flask was sealed with a rubber septum and removed from the drybox, connected to a nitrogen bubbler, and cooled to −45° C. in a liquid N₂/chlorobenzene cooling bath. Separately, 32.2 mL of 1.6 M n-butyl lithium (51.2 mmol) in hexane was charged to a 50 mL graduated cylinder, sealed with a septum, and removed from the dry box. The n-butyl lithium was added by cannula over about 10 min to the isopropyl amine at −45° C. This mixture was stirred 0.5 h. The solution was nearly clear and light yellow.

In the dry box a scintillation vial was charged with 11 g (46.8 mmol) of Bu₂SnH₂ and diluted with 25 mL of THF. The LDA solution in a rubber septum-capped flask was maintained at −45° C. in the liquid N₂/chlorobenzene bath and the Bu₂SnH₂ was added via cannula over 10 min. The entire mixture was maintained at −45° C. for 0.5 h. 5.19 g (49 mmol) of benzaldehyde was charged to a scintillation vial in the drybox and diluted with 20 mL of THF. The vial was septum sealed, removed from the drybox, and the solution was added via cannula over 10 min to the −45° C. solution of Sn lithiate solution. This mixture was stirred for 1 h at −45° C. After 20 min the mixture was taken into the dry box and placed in the dry box freezer and stored at −30° C. overnight. The mixture was taken out of the dry box freezer the next morning, charged with 60 mL of nitrogen sparged hexane followed by 60 mL of nitrogen sparged, saturated aqueous NH₄Cl. The reaction was stirred briefly, allowed to settle, and decanted. The THF/hexane layer was taken back into the dry box and evaporated to an oil. The oil was extracted into pentane and filtered through a medium glass frit into a tared round bottom flask. The pentane was removed under vacuum to leave a hazy pale yellow oil: 15.5 g. 9.45 g of the crude oil was chromatographed in 2 to 3 g portions as follows. A 12″×1″ column filled to 7 inches with silica gel 60, 230-400 mesh, was utilized. Two column eluents were used. The first eluent was comprised of 20% ethyl acetate by volume and 80% hexane by volume. The second eluent was 100% ethyl acetate. The solvents used were reagent grade from EM Sciences and were sparged with dry nitrogen using a fritted glass filter stick over ½ hour to deoxygenate them prior to transport into the dry box and use as eluent. The silica gel was degassed under high vacuum (˜20 millitorr) for 16-18 hours before use. The column was packed by pre-mixing the silica gel with the 80/20 hexane ethyl acetate and pouring the slurry into the column. All chromatography was performed in the dry box under nitrogen. The column was eluted by gravity feed and 1-4 mL aliquots of eluent were collected in glass scintillation vials. Progress was monitored using thin layer chromatography on each of the vial aliquots. Two distinct fractions were collected by combining aliquots using the 80/20 hexane/ethyl acetate eluent and a third fraction was obtained by elution with 100% ethyl acetate.

Fraction 1: Mixture of cyclic (Bu₂Sn)_(n) n=5.6. Net wt.=1.1 g, ¹¹⁹Sn NMR (C₆D₆, 186.7 MHz): −200.5 (s, J_(SnSn)=450 Hz, 471 Hz); −201.4 (s, J_(SnSn)=463 Hz)

Fraction 2: Mixture of Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂ and Bu₂[Ph(OH)CH]SnSn(Bu)₂Sn[CH(OH)Ph]Bu₂, Net wt.=4.08 g, TLC shows traces of the faster eluting cyclic compounds (Bu₂Sn)_(n) n=5.6 so a portion of fraction 2 was rechromatographed to give cyclic-free material. ¹H NMR (C₆D₆, 500 MHz): 0.7-1.95 (m, 27H, Bu); 2.6 (s, 0.27H, J_(SnH)=66 Hz, CH(OH)Ph, Sn₃ complexes); 3.16, 3.25 (s, s, 0.71H, J_(SnH)=66 Hz, CH(OH)Ph, Sn₂ complexes, 1:1 mixture of racemic pair and meso compound); 5.28 (m, 1H, CH(OH)Ph, Sn₃ complexes and Sn₂ complexes, 1:1 mixture of racemic pair and meso compound); 6.9-7.5 (m, 7.2H, Ph+C₆D₅H). ¹¹⁹Sn NMR (C₆D₆, 186.7 MHz): −48.15 (s, Bu₂[Ph(OH)CH]SnSn(Bu)₂ Sn[CH(OH)Ph]Bu₂, Sn satellites are too small to see); −48.7, −51.5 (s, s, Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂, J_(SnSn)=1674 Hz, 1651 Hz, 1:1 mixture of racemic pair and meso compound); −52.35 (s, Bu₂[Ph(OH)CH]SnSn(Bu)₂ Sn[CH(OH)Ph]Bu₂, Sn satellites too small to see). Based on relative peak heights, the mixture is 88 mole % Sn₂ complexes. The proton integration which shows 71 mole % Sn₂ complexes is probably more accurate. Reverse Phase HPLC/GC of a mixture of the two compounds allowed separation and identification of the peaks for the dimer and trimer. Column Zorbax Eclipse XDB-C18, 2.1×50 mm, A=water+0.05% trifluoroacetic acid, B=acetonitrile+0.05% trifluoroacetic acid. Program: 95% A to 0% A over 4.5 min, hold 3.5 min, then return to initial conditions, 0.8 mL/min, 60° C., 1 microliter injection. 7.157-7.223 min (897.2, largest peak, Bu₂[Ph(OH)CH]SnSn(Bu)₂Sn[CH(OH)Ph]Bu₂-OH), 6.143-6.210 min (663.1, largest peak, Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂-OH). Both compounds appear to be protonated and lose H₂O to give a stable cation in the mass spectrometer. Fraction 3: Bu₂Sn[CH(OH)Ph]₂/benzyl alcohol mixture, Net wt.=1.13 g. ¹H NMR (C₆D₆, 500 MHz): 0.7-2.0 (m, Bu); 2.55, 2.80 (s, s, —CH(OH)Ph, J_(SnH)=60 Hz, 31:69 ratio, mixture of racemic pair and meso compound), 4.30 (s, PhCH ₂OH); 5.25 (s, —CH(OH)Ph, J_(SnH)=21 Hz), 6.8-7.5 (m, C₆ H ₅C(OH)H+C₆ H ₅CH₂OH+C₆D₅H). ¹¹⁹Sn NMR (C₆D₆, 186.7 MHz): −71.0, −71.7 (s, s, 31:69 ratio, mixture of racemic pair and meso compound).

Example 8 Synthesis of an Orthoester Protected Mixture of Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂ and Bu₂[Ph(OH)CH]SnSn(Bu)₂Sn[CH(OH)Ph]Bu₂

Under nitrogen, a 50 mL Schlenk flask with a magnetic stir bar was charged with a chromatographically purified mixture of Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂ and Bu₂[Ph(OH)CH]SnSn(Bu)₂Sn[CH(OH)Ph]Bu₂ (2.27 g, Fraction 2 above), trimethylorthoacetate (30 mL), and acetic acid (5 drops). The resulting solution was heated to 80-100° C. and stirred for approximately 2 h. It was then cooled to room temperature, filtered through a 0.2 μm PTFE syringe filter and concentrated under vacuum to afford the orthoester protected mixture as a pale yellow oil (2.42 g). Idealized formulas: Bu₂{Ph[Me(MeO)₂CO]CH}SnSn{CH[OC(OMe)₂Me]Ph}Bu₂ and Bu₂{Ph[Me(MeO)₂CO]CH}SnSn(Bu)₂Sn{CH[OC(OMe)₂Me]Ph}. The crude material was used without further purification. The ¹H NMR spectrum is very complex as expected for a dimer/trimer mixture, each of which consists of a mixture of meso and racemic pairs due to the two chiral centers in each molecule (C₆D₆, 500 MHz): 0.8-2.0 (m, Me, Bu); 2.9-3.2 (m, OMe); 5.3-5.9 (m, CH[OC(OMe)₂Me]Ph); 6.8-7.4 (m, Ph+C₆D₅H).

Examples 9 and 10 Coating Mixtures Prepared from Example 8

The coating mixtures used for Examples 9 and 10 are shown below. The quantities are in grams. For each of the examples, the constituents of Portion 1 were charged into a mixing vessel in the order shown above and mixed; then Portion 2 was charged into the mixing vessel and thoroughly mixed with Portion 1 to form each of examples. Each of the coating compositions was applied with a doctor blade over a separate phosphated cold roll steel panel primed with a layer of PowerCron® Primer supplied by PPG, Pittsburgh, Pa., to a dry coating thickness of 50 micrometers and air dried at ambient temperature conditions. The panels were then tested using the tests shown in Table 1.

Example: 9 10 Portion 1 Oligomer 1# 30 30 Butyl Acetate 14.69 16.08 Flow Additive* 0.44 0.44 DBTDL solution** 2.17 0 Acetic acid 0.11 0.11 Portion 2 Desmodur 3300A*** 19.47 17.89 Catalyst Solution**** 0 2.36 #“Oligomer 1” composition is that of procedure #2 of US 6,221,494 B1, but made at 80% solids in Methyl amyl ketone *20% BYK 301 ® flow additive in Propylene glycol monomethyl ether acetate supplied by BYK-CHEMIE, Wallingford, Connecticut. **1% Dibutyltin dilaurate in methyl ethyl ketone supplied by Elf-Atochem North America, Inc. Philadelphia, Pennsylvania. ***Desmodur 3300A is an Isocyanurate trimer of hexamethylene diisocyanate supplied by Bayer. ****Catalyst solution comprising 2.42 g of the catalyst mixture from example 8 blended with 65.42 g Desmodur 3300A and 29.5 g butyl acetate.

Testing of Coating Example 10

Example 10 employed the air-activated catalysts of the present invention. Example 9 was a comparative example using a conventional dibutyltin dilaurate catalyst. From the comparative data in Table 2 it can be seen that, when used in isocyanate crosslinked coatings, the catalysts of the present invention showed improved early cure properties such as:

-   -   Improved BK4 dry times     -   Improved water spot resistance     -   equivalent hardness

These improved early cure properties will lead to improved productivity in automotive refinish body shops using ambient cured coatings.

In addition to improved cure properties, the catalysts of the present invention possess improved time to gel (more than 40% longer than a conventional tin catalyst such as Dibutyltin dilaurate); this will result in coatings that have a longer useful “pot life.” “Pot life” is the time, after activation, during which a coating can be spray applied to give good appearance and handling in an automotive refinish body shop.

TABLE 2 Ex. 9 Oligo*. 1 Ex. 10 500 ppm DBTDL & Oligo. 1 Test 2600 ppm of acetic 1350 ppm of latent catalyst & Catalyst acid 2600 ppm of acetic acid Cal. Wt. Sol. 65 65 Time to Gel. (min) 150 219 BK3 TIME (min) 179 162 BK4 TIME (min) >348 256 APP/ V. Good V. Good Clarity WATER SPOT 4 HR RT 7 9 1 DAY RT 9 10 MEK RUBS 4 HR RT 650 600 1 DAY RT 700 700 PERSOZ HARD 4 DAY RT 21 19 1 DAY RT 90 73 FISHER HARD 1 DAY RT 11.68 9.9 7 DAY RT 83 63 *Oligo. is an abbreviation for Oligomer

Example 11 Synthesis of Bu₃SnCH(OSiMe₃)Ph

Under nitrogen, a 100 mL flask was charged with Bu₃SnCH(OH)Ph (1.50 g, 3.79 mmol) and anhydrous acetonitrile (10 mL). To the resulting solution was added N,O-bis(trimethylsilylacetamide) (0.46 g, 2.27 mmol) dropwise. The reaction mixture was heated and stirred at reflux for 1 h. It was then allowed to cool to room temperature and stirred overnight. The reaction mixture was concentrated to dryness, and the crude product extracted with hexane. The hexane extract was concentrated to dryness to afford Bu₃SnCH(OSiMe₃)Ph as a yellow oil (1.10 g, 62%). The crude material was used without further purification.

Example 12 Synthesis of a Mixture of Bu₂[Ph(OSiMe₃)CH]SnSn[CH(OSiMe₃)Ph]Bu₂, Bu₂[Ph(OSiMe₃)CH]SnSn(Bu)₂Sn[CH(OSiMe₃)Ph]Bu₂

Under nitrogen, a 50 mL flask was charged with a solution of Bu₂[Ph(OH)CH]SnSn[CH(OH)Ph]Bu₂ and Bu₂[Ph(OH)CH]SnSn(Bu)₂Sn[CH(OH)Ph]Bu₂ (cf. Example 7, 0.400 g, ˜0.6 mmol) and 10 mL acetonitrile. To this was added N,O-bis(trimethylsilyl)acetamide (0.144 g, 0.71 mmol) dropwise. The resulting reaction mixture was heated and stirred at reflux for 1 h. The reaction mixture was concentrated to dryness, and the crude product extracted with hexane. The hexane extract was concentrated to dryness to afford a mixture of Bu₂[Ph(OSiMe₃)CH]SnSn[CH(OSiMe₃)Ph]Bu₂ and Bu₂[Ph(OSiMe₃)CH]SnSn(Bu)₂Sn[CH(OSiMe₃)Ph]Bu₂ as an oil (0.27 g). The crude material was used without further purification.

Examples 13-17 Silyl-Protected α-Hydroxybenzylstannane Catalysts

The procedures described above for Examples 1-6 were followed, except that the protecting group included silyl functionality. The results are shown in Table 3 below.

As is true of other protected α-hydroxybenzylstannane compounds, Bu₃SnCH(OSiMe₃)Ph is not air-sensitive and is a catalyst for urethane formation. Unlike Bu₃SnCH[OC(OMe)₂Me]Ph, however, it is not latent (Table 3, example 13). Addition of acetic acid results in shorter BK4 dry times and longer gel times, but there is still no evidence of latency (examples 14 and 15). A mixture of Bu₂[Ph(OSiMe₃)CH]SnSn[CH(OSiMe₃)Ph]Bu₂ and Bu₂[Ph(OSiMe₃)CH]SnSn(Bu)₂Sn[CH(OSiMe₃)Ph]Bu₂ is a latent catalyst (Table 3, example 16), although even in the absence of air a high level of activity is observed. The addition of acetic acid shortens the BK4 time and lengthens the gel times; the system is still latent with the gel time under air being only half of that under nitrogen (Table 3, example 17).

TABLE 3 Silyl-protected α-hydroxybenzylstannane catalysts (TMS≡SiMe₃) BK4 Ex. No. Catalyst Gel Times Time Comments 13 Bu₃SnCH(OSiMe₃)Ph    2.3 h (air) 9.6 h Freshly prepared 0.53 mmol    2.3 h (N₂) sample; no acid 14 Bu₃SnCH(OSiMe₃)Ph    6.0 h (air) 3.6 h 5 equiv AcOH 0.53 mmol    5.8 h (N₂) added 15 Bu₃SnCH(OSiMe₃)Ph  >7.5 h (air) 4.1 h 10 equiv AcOH 0.53 mmol  >7.5 h (N₂) added 16

  1.15 h (air)   2.25 h (N₂) (0.061 mmol catalyst) 2.2 h (0.061 mmol catalyst) Freshly prepared sample; no acid 17

   2.3 h (air)    4.2 h (N₂) (0.061 mmol catalyst) 1.3 h (0.061 mmol catalyst) 10 equiv AcOH added ¹Conditions: 23.7 g 351P11111, 9.73 g Desmodur ® 3300, catalyst, ambient temperature. 

1. A process for polyurethane synthesis comprising the steps of: a) providing a catalyst of the formula R¹ _(a)R² _(b)R³ _(c)Sn[CH(OX)R⁴]_(d), wherein R¹, R², and R³ are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group, R⁴ represents an optionally substituted hydrocarbyl or optionally substituted aryl group, a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid-labile or moisture-labile protecting group; b) contacting at least one isocyanate with the catalyst of step a) to form a blend; c) contacting the blend of step b) to at least one polyol to form a mixture; and d) optionally exposing the mixture of step c) to air or a gas comprising oxygen.
 2. The process of claim 1, wherein the polyol of step c) further comprises an acid.
 3. The process of claim 2, wherein the acid is acetic acid.
 4. A process for polyurethane synthesis comprising the steps of: a) providing a catalyst of the formula R¹ _(a)R² _(b)R³ _(c)Sn[CH(OX)R⁴]_(d), wherein R¹, R², and R³ are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group, R⁴ represents an optionally substituted hydrocarbyl or optionally substituted aryl group. a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid-labile or moisture-labile protecting group; b) contacting at least one polyol with the catalyst of step a) to form a blend; c) contacting the blend of step b) to at least one isocyanate to form a mixture; and d) optionally exposing the mixture of step c) to air or a gas comprising oxygen.
 5. The process of claim 4, wherein the isocyanate of step c) further comprises an acid.
 6. The process of claim 5, wherein the acid is acetic acid.
 7. The process of claim 1 or 4, wherein said X protecting group is selected from the group consisting of C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.
 8. The process of claim 1 or 4, wherein said catalyst is represented by the formula

wherein each X is a protecting group independently selected from the group consisting of C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.
 9. The process of claim 1 or 4, wherein the catalyst is represented by the formula

wherein each X is a protecting group independently selected from the group consisting of C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.
 10. The process of claim 1 or 4, wherein the catalyst is represented by the formula

wherein each X is a protecting group independently selected from the group consisting of C(OR⁵)₂R⁶, SiR⁷ ₃, and C(O)R⁸, wherein R⁵, R⁶, R⁷ and R⁸ are alkyl, substituted alkyl or aryl.
 11. The process of applying a coating to a substrate comprising: (i) providing the mixture synthesized by the process of claim 1 or 4; (ii) optionally adding to the mixture of step (i) at least one additive selected from the group consisting of functionalized oligomers, binders, pigments, stabilizers, rheology control agents, flow agents, toughening agents, fillers and combinations thereof; (iii) optionally adding the mixture of step (i) or step (ii) at least one solvent selected from the group consisting of aromatic hydrocarbons, petroleum naphtha, xylenes, ketones, methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone, acetone, esters, butyl acetate, hexyl acetate, glycol ether esters, propylene glycol monomethyl ether acetate and combinations thereof; (iv) applying the mixture to the substrate to form the coating.
 12. The process as recited in claim 11, wherein the applying is selected from the group consisting of spraying, electrostatic spraying, roller coating, dipping and brushing.
 13. The process as recited in claim 11, wherein the substrate is selected from the group consisting of automobiles, automobile bodies, frame rails, trucks, truck bodies, buses, farm and construction equipment, truck caps, truck covers, trailers, recreational vehicles, motor homes, campers, vans, snow mobiles, all terrain vehicles, motorcycles, bicycles, boats, airplanes, aircraft, cement floors, wood floors, concrete surfaces, wood substrates, parking lots, drive ways, asphalt surfaces, bridges, towers, coil coating, railroad cars, printed circuit boards, signage, fiberglass structures, sporting equipment, and golf balls.
 14. The process of applying a coating composition to a substrate comprising: (i) providing the a mixture synthesized by the process of claim 7; (ii) optionally adding to the mixture of step (i) at least one additive selected from the group consisting of functionalized oligomers, binders, pigments, stabilizers, rheology control agents, flow agents, toughening agents, fillers and combinations thereof; (iii) optionally adding to the mixture of step (i) or step (ii) at least one solvent selected from the group consisting of aromatic hydrocarbons, petroleum naphtha, xylenes, ketones, methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone, acetone, esters, butyl acetate, hexyl acetate, glycol ether esters, propylene glycol monomethyl ether acetate and combinations thereof; (iv) applying the mixture to the substrate to form the coating.
 15. The process as recited in claim 14, wherein the applying is selected from the group consisting of spraying, electrostatic spraying, roller coating, dipping and brushing.
 16. The process as recited in claim 14, wherein the substrate is selected from the group consisting of automobiles, automobile bodies, frame rails, trucks, truck bodies, buses, farm and construction equipment, truck caps, truck covers, trailers, recreational vehicles, motor homes, campers, vans, snow mobiles, all terrain vehicles, motorcycles, bicycles, boats, airplanes, aircraft, cement floors, wood floors, concrete surfaces, wood substrates, parking lots, drive ways, asphalt surfaces, bridges, towers, coil coating, railroad cars, printed circuit boards, signage, fiberglass structures, sporting equipment, and golf balls. 